You could do this, which will give you far more control over your Posts Feature slider images etc..

Go to Wordpress Admin Dashboard > PageLines > Site Options

The go to Advanced and check the option for "Feature Section - Enable "Post-As-Feature" Control Metapanel"

Once enabled, this will add a new set of options on your posts.

Go to your posts and then scroll down past the PageLines Meta Settings, you will see these new options. It will give you more control over your posts when being added to your feature slider and allow you to add a custom image that will only appear in the slider and have no effect on your post.

Thanks for the help. I already had that activated and have tried both static height and fixed height with the adjustment of aspect mode-ratio. Nothing seems to help stop the stretching of the picture and the resulting poor resolution of the picture.

Do you have any other ideas?

PS: Is there any way to adjust the width of the title section of the feature screen? Some of my longer post titles are cut off.

The best options would be to use Danny suggestion of uploading a higher resolution image into the feature slider using the meta settings, and keeping the original lower resolution image for inserting into the post.

You can control the width of the content overlay in the feature slider by inserting the following css into Pagelines>Site Options>Custom Code. Change the % to whatever you feel looks best